The present invention relates to a system for treating and controlling blow-by gas in the crankcase of an internal combustion engine and, more particularly, to a blow-by gas treating and controlling system having a blow-by gas pipe interconnected between the cylinder head cover of the engine and the carburetor barrel to ventilate the cylinder head cover and, hence, the crankcase. Still more particularly, the invention is concerned with a blow-by gas treating and controlling device of the kind described, wherein the blow-by gas treating pipe is connected directly to the vacuum area of the throttle barrel of variable venturi or other carburetor upstream from the throttle valve, without making use of a PCV valve so that the blow-by gas is induced by the vacuum which is generated in accordance with the flow rate of intake air-fuel mixture, the system further having a bleed pipe interconnected between the blow-by gas treating pipe and the air cleaner of the engine to maintain a balance of pressure in the crankcase.
As is well known, in the internal combustion engine, a so-called blow-by gas is emitted in the crankcase as a result of leaks of intake air-fuel mixture and combustion gas through the clearances around piston rings, during compression and combustion or exhaust cycle. Crankcase forced ventilation systems cycle the blow-by gas and burning the same together with the intake air-fuel mixture. In fact, there is a trend in various countries to develop such a system and to enact a regulation for the equipment of such a system.
Hitherto, it has been clarified that the blow-by gas generally has the following features.
(1) The blow-by gas is an admixture of the intake air-fuel mixture and the combustion gas, the rate of mixing being 85:15. Thus, the major component of the blow-by gas is the air-fuel mixture which is combustible.
(2) The blow-by gas contains 20,000 ppm of hydrocarbon which amounts to an air-fuel ratio of 15.
(3) Ten (10) liters of blow-by gas contains about 0.5 gr of water content.
(4) The water component exhibits a PH value of 2. Further, 200 to 400 ppm of SO.sub.4.sup.-- and 30 to 60 ppm of Cl.sup.-- are contained by the blow-by gas.
FIG. 1 shows a typical conventional blow-by gas ventilation system making use of a PCV valve and the vacuum established in the intake manifold. More specifically, the head cover 3 of cylinder head 2 of an engine 1 is communicated with an intake manifold 4 through a blow-by gas ventilation pipe 5 to the base portion of which attached is a so-called PCV valve (Positive Crankcase Ventilation Valve) which is known per se and designated at a reference numeral 6. Also, a bleed pipe 8 is connected to the air cleaner 7. The arrangement is such that the blow-by gas 9 from the crank chamber is induced as shown by a full line so as to be mixed with the fresh mixture supplied through the carburetor and burnt together with the fresh mixture.
Since the operation of this known system relies upon the vacuum P in the intake manifold, the flow rate Q.sub.1 of the gas flowing through the PCV valve 6 is greater than rate Q.sub.2 of accumulation of the blow-by gas in the operation range over the idling region I and medium load region M, so that fresh air-fuel mixture is introduced into the crankcase 12 at a rate B, while the blow-by gas is induced at a rate A into the intake manifold 4 through the PCV valve 6 and the blow-by gas treating pipe 5. In the full-load region F, the rate of discharge of the blow-by gas is increased naturally, whereas the flow rate of the gas flowing through the PCV valve 6 is reduced because of reduction of the intake manifold. As a countermeasure for compensating for the reduction of the flow rate of the gas, the blow-by gas is expelled from the crank chamber 12 to the air cleaner 7 through a bleed pipe 8, so that the blow-by gas is mixed with the fresh mixture introduced through the carburetor 10 and burnt together with the fresh mixture.
Thus, this system has flexibility to change the path of blow-by gas in accordance with the state of operation of the engine corresponding to the level of load imposed thereon. This system, however, has various disadvantages. Namely, the oil mist and/or moisture contaminates or blocks small holes such as that of the air bleed, as the blow-by gas flows through the carburetor from the air cleaner, resulting in an undesirable change of air-fuel ratio characteristic of the engine.
At the same time, oil mist and moisture attach to the air cleaner element or to the inside of the air cleaner to increase the filtration resistance resulting not only in the reduction of the engine output but also an icing in the small venturi portion of the carburetor to hinder the smooth operation of the engine.
In case of a variable-venturi type carburetor, the smooth movement of the suction piston is lost due to the attaching of oil mist and water. In the worst case, the suction piston becomes immovable due to sticking.